Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.
Peanut allergy is a life-threatening and incurable disorder, affecting approximately 1% of the general population (Sicher et al., J Allergy Clin Immunol 103: 559-562, 1999). It is characterised by the sudden onset of anaphylaxis, which may occur with exposure to minute quantities of peanut proteins (Hourihane et al., J Allergy Clin Immunol 100: 596-600, 1997). Nut induced anaphylaxis is that most frequently associated with mortality or with life-threatening features (Sampson et al, N Engl J Med 327: 380-4, 1992). Peanut proteins are frequently concealed within apparently safe food sources, such that accidental contact occurs for up to 50% of sufferers over a 5 year period (Sicherer et al., Paediatrics 102: e6, 1998). Not surprisingly, nut allergy is associated with significant psychological morbidity for sufferers and carers alike, akin to that suffered by those with chronic debilitating illnesses such as rheumatoid arthritis (Primeau et al., Clin Exp Allergy 30: 1135-43, 2000). Cure, while being an imperative to remove nut allergy as a cause of mortality, is also necessary to remove the chronic psychological burden that peanut allergic subjects carry.
To date, efforts at immunotherapy for peanut allergy have been met by extremely limited success. Nelson et al. have shown that tolerance of peanut can be induced using a rush immunotherapy protocol, but that tolerance is lost in approximately half of the subjects during maintenance dosing and additionally that injections are associated with frequent episodes of anaphylaxis in the majority of subjects during both the buildup and maintenance phases (Nelson et al., J Allergy Clin Immunol 99: 744-51, 1997). Oppenheimer et al. demonstrated similar findings within their study, again showing that active therapy is associated with a high rate of systemic anaphylaxis. Data collection in that study was terminated after the administration of peanut extract to a placebo randomised subject resulted in their death, highlighting the dangerous nature of this condition (Oppenheimer et al., J Allergy Clin Immunol 90: 256-62, 1992).
Development of novel strategies to overcome the morbidity associated with allergen immunotherapy depends on an accurate understanding of the immunological basis to successful immunotherapy, as well as its side-effects. It has long been established that morbidity due to allergen immunotherapy is due to the cross-linking of IgE, and that this action is not required for such therapy to be efficacious (Litwin et al., Int Arch Allergy Appl Immunol 87: 361-61, 998). It is also known that one of the critical actions of immunotherapy in producing tolerance is its ability to change the predominant specific T cell phenotype from a TH2 to a TH1 phenotype (Robinson, Br Med Bull 56: 956-968, 2000). Although the precise pathway through which this change occurs remains undocumented, current theories suggest that this is likely to occur via the suppression of the TH2 phenotype by IL-10, then reconstitution of a normal immune response via the actions of IL-2 and IL-15 (Akdis et al., Allergy 55: 522-530, 2000).
A key difference in antibody and lymphocyte responses is in antigen recognition, antibodies recognising conformational epitopes dependent on molecular tertiary structure, while CD4+ T cells recognise short linear peptides. This difference in antigen recognition is the basis to many novel strategies of immunotherapy, including that using peptides based upon T cell epitopes, B cell epitope mutants and altered peptide ligands (Akdis et al., Trends Immunol 22: 175-8, 2001). Such methods all depend on the alteration or absence molecular tertiary structure, so that IgE cross-linking and effector cell activation is lost. Peptide immunotherapy is the method for which the best evidence of efficacy exists, being documented for both cat dander allergy and bee venom allergy. Muller et al. (1998) showed that, in the absence of any systemic side-effects, tolerance could be achieved for the major bee venom allergen Phospholipase A2 (PLA2) using sequences based on its three major epitopes, while several authors have demonstrated that peptides based on the structure of the major cat allergen Fel d 1 can be used to induce diminished-clinical responses (Muller et al., J Allergy Clin Immunol 101: 747-754, 1998; Norman et al., Am J Respir Crit Care Med 154: 1623-8, 1996; Marcotte et al., J Allergy Clin Immunol 101: 506-13, 1998; Pene et al., J Allergy Clin Immunol 102: 571-8, 1998; Maguire et al., Clin Immunol 93: 222-31, 1999). Crucial to the development of such strategies is the retention of T cell epitopes, so that T cell phenotypic change can be induced.
Accordingly, there is a need to both identify the major peanut allergens and, further, to identify the T cell epitopes of these allergens. The identification characterisation, and analysis of these epitopes is critical to the development of specific diagnostic and immunotherapeutic methodology.
In work leading up to the present invention, the inventors have identified the human T cell epitopes of the peanut allergen, Ara h 2. The identification of Ara h 2 T cell epitopes now facilitates the development of molecules and methodology for the diagnosis and treatment of conditions characterised by the aberrant, inappropriate or otherwise unwanted immune response to Ara h 2 or derivative or homologue thereof such as peanut allergy or other tree-nut allergy.